This invention relates to a stable aromatic amine composition comprising an aromatic amine group containing compound and a small quantity of a carboxylic acid. The present invention also relates to a method for preventing the discoloration of aromatic amine group containing compounds, and to a process for the production of light colored aromatic amine based polyether polyols.
One of the problems or disadvantages associated with amine group containing compounds is the tendency of these compounds to discolor.
Discoloration of some amine group containing compounds such as, for example, ortho-toluenediamine (o-TDA), darken quickly upon exposure to air, while others such as, for example, aniline, are more stable and darken slower over time. The aliphatic amine group containing compounds also discolor over time at room temperature, but generally speaking, these discolor at a much slower rate than the aromatic amine group containing compounds.
U.S. Pat. No. 3,595,918 relates to the stabilization of tolylene diamine. This reference discloses that tolyenediamine can be stablized against discoloration by the addition of an ascorbic acid in an amount of 0.05% to about 5% by weight. Ascorbic acid, isoascorbic acid and their mixtures are the only compounds disclosed as being suitable for stabilizing tolyene diamine. These two compounds are actually cyclic lactones, not free carboxylic acids.
Amine group containing compounds are known to be suitable initiators for preparing polyether polyols. Various amine initiated polyether polyols and the process for their production are described in, for example, U.S. Pat. Nos. 3,264,268, 3,314,995, 3,446,848, 3,462,492, 3,499,009, 4,209,609, 4,391,728, 4,421,871 and 4,562,290, and as described in British Patents 1,073,664, 1,311,095 and 1,398,185.
U.S. Pat. No. 4,877,879 describes the stabilization of polyether polyols prepared from amine initiators in the presence of alkaline catalysts. This reference suggests that the addition of an excess amount of a reducing agent, particularly formic acid, is effective in neutralizing the alkaline catalyst, thereby stabilizing the reactivity of the polyether polyol. This is described as being particularly effective for aliphatic amine initiators containing a tertiary nitrogen as the resultant polyether reacts with an alkylene oxide to yield a dark, color-forming quaternary amine complex.
The use of discolored amine group containing compounds as initiators in the production of polyether polyols results in the polyether polyols also being discolored. The dark color of the resultant polyether polyols is irreversible. Therefore, a means of preventing discoloration of amine group containing compounds and/or reducing the color of polyether polyols started from amine group containing compounds are commercially desirable.
One way of avoiding/preventing discoloration of these amine group containing compounds and polyether polyols prepared from these compounds, is to immediately form polyether polyols from the amine group containing compounds after distillation, before they come into contact with air. This, however, requires that the amine group containing compounds and the resultant polyether polyols be produced in the same plant, with no time lapse between the point of distilling the amine containing compounds and when these are used as initiators to form polyether polyols. Otherwise, stringent engineering measures are required to ensure that the amine compounds are oxygen-free at all points in the process between the time they are purified and used. Currently, it is necessary to keep the entire process totally under nitrogen to prevent and/or minimize this discoloration.
In accordance with the present invention, it was found that the addition of a relatively small quantity of certain groups of compounds to aromatic amine compounds surprisingly formed compositions which are stable against discoloration. This is true even after storing the treated aromatic amine compositions in a 100.degree. C. oven for 1 week. Polyether polyols can then be produced from these treated aromatic amine compounds, without the derogatory color effects one would normally expect.